Steroids for terminally ill cancer patients

Wow. I wonder now if Decadron may be contributing to my partner's increased irritablity and anger. He gets Decadron as a pre-med infusion every two weeks as part of his chemotherapy treatments. He was also taking Decadron pills for a couple days after chemo, but stopped that (with his oncologist's blessing) a couple of treatments ago. He still gets the black hole appetite though and over the past few weeks has become for angry an intollerant of any mistakes that I or anyone else makes. Does anyone know how long it takes for the Decadron side effects to dissappear?